Bladder

Structure

The bladder wall has three muscle layers collectively called the detrusor, lined inside by a stretchable transitional epithelium. The trigone marks where the ureters enter and the urethra leaves.

Function

As filling progresses, stretch receptors signal the central nervous system, producing the sensation of need to void. Coordinated detrusor contraction and sphincter relaxation produce urination.

Variants

The term also refers to the gallbladder, which stores bile, and to the air bladder of some species; in human anatomy gum context the urinary bladder is meant.